/*
 * SHA1 T-PRF for EAP-FAST
 * Copyright (c) 2003-2005, Jouni Malinen <j@w1.fi>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 */

#include "includes.h"

#include "common.h"
#include "sha1.h"
#include "crypto.h"

/**
 * sha1_t_prf - EAP-FAST Pseudo-Random Function (T-PRF)
 * @key: Key for PRF
 * @key_len: Length of the key in bytes
 * @label: A unique label for each purpose of the PRF
 * @seed: Seed value to bind into the key
 * @seed_len: Length of the seed
 * @buf: Buffer for the generated pseudo-random key
 * @buf_len: Number of bytes of key to generate
 * Returns: 0 on success, -1 of failure
 *
 * This function is used to derive new, cryptographically separate keys from a
 * given key for EAP-FAST. T-PRF is defined in RFC 4851, Section 5.5.
 */
int sha1_t_prf(const u8 *key, size_t key_len, const char *label,
        const u8 *seed, size_t seed_len, u8 *buf, size_t buf_len)
{
    unsigned char counter = 0;
    size_t pos, plen;
    u8 hash[SHA1_MAC_LEN];
    size_t label_len = os_strlen(label);
    u8 output_len[2];
    const unsigned char *addr[5];
    size_t len[5];

    addr[0] = hash;
    len[0] = 0;
    addr[1] = (unsigned char *) label;
    len[1] = label_len + 1;
    addr[2] = seed;
    len[2] = seed_len;
    addr[3] = output_len;
    len[3] = 2;
    addr[4] = &counter;
    len[4] = 1;

    output_len[0] = (buf_len >> 8) & 0xff;
    output_len[1] = buf_len & 0xff;
    pos = 0;
    while (pos < buf_len) {
        counter++;
        plen = buf_len - pos;
        if (hmac_sha1_vector(key, key_len, 5, addr, len, hash))
            return -1;
        if (plen >= SHA1_MAC_LEN) {
            os_memcpy(&buf[pos], hash, SHA1_MAC_LEN);
            pos += SHA1_MAC_LEN;
        } else {
            os_memcpy(&buf[pos], hash, plen);
            break;
        }
        len[0] = SHA1_MAC_LEN;
    }

    return 0;
}
